This invention relates to a spool deflection indicator which is used to electrically indicate the change in position of a spool or piston. Such a spool deflection indicator is used in different types of control systems and has particular applicability to those found in aircraft.
The spool deflection indicator generally employs a standard switch which operates by depressing a switch button. Because of the manner in which the spool deflection indicators are used, the switch must change modes, thereby passing the proper signal, each and every time the spool moves beyond a certain specified distance in either direction. The allowable distance is usually very small and, therefore, the spool deflection indicator must reliably transfer this very small movement of the spool to the switch button so that it is depressed. Due to the fact that the spool deflection indicator may be used as part of an aircraft control system, reliability is of paramount importance.
As the distance required for the spool to travel before it triggers the switch is not the same in different control systems, it is desirable that the particular indicator be easily adjustable so that the same type can be used in a variety of situations. Along this same line, it may also be very useful in any particular instance to be able to adjust the sensitivity of an individual unit. Furthermore, since the spool and at least a portion of the indicator are generally immersed in a fluid under pressure, the spool deflection indicator must also reliably operate under these same conditions and be sealed to prevent leakage. These factors increase the design problems encountered in this area.
As a result of the degree of accuracy needed and the miniscule action upon which operation depends, along with the other design factors, no known prior art spool deflection indicator successfully meets the requirements of sensitivity and reliability which are demanded.